1. Field of the Invention
The present invention relates to a self-compensating dynamic balancer, and more particularly, to a self-compensating dynamic balancer having an improved structure so that the time required for balancing can be reduced and balancing performance can be improved when a rotating body rotates in a vertical direction.
2. Description of the Related Art
In general, a disk player records/reproduces information on/from an optical disk in a non-contact method. As the rotational speed of a spindle motor installed in the disk player increases, detrimental internal vibrations may be generated. The internal vibrations are generated mainly due to the revolution of the rotation center of a rotating body, that is, whirling, which is caused by disparity between the rotation center and the center of mass of the rotating body. The eccentric mass of the rotating body is produced by an error in a manufacturing process of the rotating body such as a disk. Thus, a self-compensating dynamic balancer is adopted to reduce the internal vibrations.
FIGS. 1 and 1A show a conventional self-compensating dynamic balancer for reducing internal vibrations. The self-compensating dynamic balancer consists of a case 10 and a plurality of rigid bodies 40 provided in the case 10. The case 10 includes a main body 20 having a circular race 21 in which the rigid bodies 40 are placed and a cover member 30 covering an open portion of the main body 20.
A coupling hole 35 for coupling a rotation shaft 51 of a driving source 50 to the case 10 is formed at the center of the cover member 30. The circular race 21 is a space in which the rigid bodies 40 can freely move and is concentric with the center of the coupling hole 35. Thus, when the case 30 rotates, the rigid bodies 40 located in the race 21 tend to move away from the rotation center of the rotation shaft 51 due to a centrifugal force. In this case, when the rotation shaft 51 revolves due to eccentric mass, the rigid bodies 40 are located opposite to the center of mass with respect to the rotation shaft 51 so that the internal vibrations due to the eccentric mass can be reduced.
In the self-compensating dynamic balancer having the above structure, the diameter of a circle made by the circular race 21, the diameter and mass of each of the rigid bodies 40, and the number of rigid bodies 40 are determined considering a normal rotation speed of a rotating body such that the internal vibrations due to the unbalanced mass of the rotating body are reduced.
In the conventional self-compensating dynamic balancer, however, while performing a balancing operation, the rigid bodies 40 do not stop quickly at balancing positions due to weak damping between the rigid bodies 40 and the race 21. Also, since the rigid bodies 40 contact surfaces of the outer wall and the bottom of the race 21, the rigid bodies 40 are easily abraded and the whole balancing performance deteriorates. Further, when fluid is injected inside the race 21 to induce strong damping, reproducibility of a balancer is lowered due to surface tension.
Also, when the above self-compensating dynamic balancer is installed vertically, since the rigid bodies 40 are naturally disposed in the lower portion of the race 21 due to the pull of gravity, it is difficult for the rigid bodies 40 to move to their balancing positions.